Purpose: Recently, we demonstrated that, contrary to predictions by classical hierarchical vision models, global context affects spatial masking (Barghout, Palmer and Tyler VSS 2002 ). Here we examine the effect of global context on masking by edge induced illusory contours on a target both consistent and inconsistent with an induced brightness illusion. Methods: We measured threshold elevation as a function of pedestal contrast (TvC) of a vertical 4 c/d micro-Gabor target in both the sine and cosine phase. Two control configurations controlled for known masking effects. The two experimental conditions manipulated global context by aligning the target with an induced illusory edge. In one condition, the target phase was not consistent with the induced brightness edge percept. In the second condition, the target phase was aligned so that it matched the brightness percept. Results: The target inconsistent with the brightness effect produced no masking or facilitation relative to our baseline control. The target consistent with the brightness percept, however, masked contrast detection and facilitated high contrast masking. Thus, global context introduced by edge induced contours effects local masking when the contrast polarity of the target is consistent with the brightness percept.